Process for direct oxidation of propylene to propylene oxide and large particle size titanium silicalite catalysts for use therein

ABSTRACT

Large crystals of titanium silicalite or intergrowths of intergrown smaller crystals, having a mean particle size greater than 2 μm, have been found catalytically effective at commercially reasonable rates for the epoxidation of olefins in the presence of hydrogen peroxide. Crystals synthesized with a silica source having a low sodium content exhibit high levels of production and selectivity. The crystals have a low attrition rate and are easily filterable from a product stream.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention pertains to the synthesis of propyleneoxide from hydrogen peroxide in the presence of a titanium silicalitecatalyst, or from hydrogen/oxygen mixtures in the presence of acommercially viable noble metal-treated titanium silicalite catalyst.

[0003] 2. Background Art

[0004] Propylene oxide is an important alkylene oxide of commerce. Largeamounts of propylene oxide are used, inter alia, for the preparation ofnonionic polyether surfactants and of polyether polyols for manufactureof polyesters and other polymers, but in particular for polyols formanufacture of polyurethanes, the latter including both homopolymericpolyoxypropylene polyols and copolymeric polyols prepared using otheralkylene oxides, particularly ethylene oxide, in addition to propyleneoxide. Propylene oxide also has numerous other uses in organicsynthesis.

[0005] Older methods of propylene oxide production employed the“epichlorohydrin” process, a process which employs toxic chlorine, andgenerates numerous chlorine-containing byproducts which presentenvironmental concerns but is still in use today. Several “coproduct”processes have been disclosed and/or implemented. In one majorcommercial process, indirect oxidation of propylene by ethylbenzeneoxidation products to form propylene oxide yields styrene as a majorcoproduct. In both this as well as other coproduct processes, theeconomic value of the coproduct has a great effect on the overallprocess economics. The value of the coproducts may at times byundesirably low. Thus, it is desirable to employ a process which doesnot rely on coproduct economics to produce propylene oxide.

[0006] A “direct” method of propylene oxide production has long beensought. In such “direct” methods, propylene oxide is produced byoxidation of propylene with oxygen or with a “simple” oxidizingprecursor such as hydrogen peroxide, without the use of significantamounts of co-reactants and concomitant generation of co-products fromthese co-reactants. Even though a great deal of research has beenexpended in these efforts, “direct” production of propylene oxide hasnot heretofore become a commercial reality.

[0007] In U.S. Pat. No. 5,401,486, it is disclosed that propylene oxidemay be produced by the “direct” oxidation of propylene by hydrogenperoxide in the presence of a titanium silicalite catalyst, citing EPA-100,118. However, the latter indicates that the principle products ofolefin oxidation are ethers, with olefin oxides prepared only in minoramounts. The titanium silicalite useful in such processes, despite therelatively low yield of olefin oxides, has been generally acknowledgedby the art to be limited to exceptionally small titanium silicalitecrystals substantially free of the anatase form of titanium silicalite.These crystals are about 0.2 μm or less in size. Since the catalysts areheterogenous catalysts, use of larger particle size catalysts, withtheir decreased surface area, should result in a considerable decreaseof activity and product yield in the oxidation of alkenes. For example,the rate of oxidation of linear alkanols employing titanium silicaliteshas been shown to be reduced as crystal size of the titanium silicaliteis increased. See, e.g., “Oxidation of Linear Alcohols with HydrogenPeroxide Over Titanium Silicalite 1,” A. Van der Pol et al., SchuitInstitute of Catalysis, Eindhoven University of Technology, APPL. CATAL.A., 106(1) 97-113 (1993), which indicates that a particle size less than0.2 microns is necessary to obtain maximum catalyst activity. See alsoU.S. Pat. No. 6,106,803, which indicates that high catalytic activitycan only be obtained with small primary crystals of titanium silicalite.The U.S. Pat. No. 6,106,803 patentees teach preparing small primarycrystals and using these crystals to form granulates of larger size byspray-drying. These and other publications have discouragedinvestigation of the use of large titanium silicalite crystals.

[0008] Other references which relate more directly to olefin epoxidationindicate that selectivity and hydrogen peroxide conversion efficiencyare decreased by the presence of anatase in the titanium silicalitecatalyst. See, e.g., “Preparation of TS-1 Zeolite Suitable forCatalyzing the Epoxidation of Propylene,” H. Gao et al., ShanghaiResearch Institute of Petrochemical Technology, Shanghai, PeoplesRepublic of China, Shiyou Xuebao, Shiyou Jiagong (2000) 16 (3), p.79-84; and “Synthesis and Physicochemical Properties of ZeolitesContaining Framework Titanium,” C. Dartt et al., California Institute ofTechnology, Pasadena, Calif., MICROPOROUS MATTER, 2 (5) p. 425-437(1994).

[0009] However, use of small titanium crystals, e.g. those having meansizes of about 0.2 μm or less is highly problematic in commercialepoxidation of alkenes. In fixed bed processes, the small particle sizecreates an enormous pressure drop which renders the process unworkable,while in slurry processes, separation of the catalyst from the liquidreactor contents is extremely difficult. Moreover, due to the attritionof particulate catalysts in commercially useful reactors, the particlesize decreases over time, eventually plugging filters designed torecover and recirculate catalyst back to the reactor. As a result,although the catalyst activity of small particle size catalysts isreasonably high, a commercial process employing such catalysts is notpractical.

[0010] To improve the longevity of the olefin epoxidation process, smalltitanium silicalite crystals have been conglomerated into formedparticles of larger size through the use of binders, as taught, forexample, by U.S. Pat. Nos. 5,500,199 and 6,106,803. However, suchconglomerated catalysts suffer from several defects. The binder, thoughporous, will necessarily obscure portions of the zeolite structure, thuseffectively removing such portions as catalytic sites in the reaction.Unless the binder has high adhesive and cohesive strength, the formedparticles will again be subject to attrition as the conglomerates breakapart. Increasing binder content can minimize attrition, although thelikelihood of obscuring catalytic sites is then higher. Moreover, thecatalyst is essentially “diluted” by the binder on a weight/weightbasis, thus requiring greater amounts of catalyst for the same epoxideproduction rate.

[0011] It would be desirable to directly epoxidize propylene in thepresence of large titanium silicalite crystals which exhibit highactivity, low attrition rates, and freedom from use of binders, andwhich do not cause rapid plugging of catalyst filter elements.

SUMMARY OF THE INVENTION

[0012] It has now been surprisingly discovered that large sized crystalsof titanium silicalite and crystal intergrowths thereof may be used inalkene epoxidation at commercially useful epoxidation rates despite theprejudice of the art against the use of such large sized particles. Ithas been further surprisingly discovered that the silica source materialcan markedly affect catalytic activity. Alkene epoxidation processesemploying large crystals and intergrowths generate fines much lessrapidly, and thus alkene epoxidations employing such catalysts can runfor extended periods without shutdown, and with considerably lessaddition of new catalyst to the process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a scanning election micrograph of titanium silicaliteintergrowths prepared according to one aspect of the invention.

[0014]FIG. 2 is a scanning electron micrograph of non-intergrown largesingle crystal titanium silicalite prepared according to a furtherembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0015] The present invention pertains to alkene epoxidation in thepresence of titanium silicalite catalyst particles having an averageparticle size of greater than 2 microns. The size of the particles canbe measured by scaling from scanning electron micrographs or via methodswhich are based on laser dispersion methods. Epoxidation in the subjectinvention process may be by hydrogen peroxide or by a mixture ofhydrogen and oxygen when a suitable noble metal-treated catalyst isused. As used herein, the term “epoxidation” refers to processes usingeither set of epoxidizing reactants set forth above unless indicatedotherwise. The use of hydrogen and oxygen may be termed an “in situ”process, since hydrogen peroxide is generated in situ. In the latterprocess, the preferred catalyst is a palladium-treated titaniumsilicalite, although other palladium catalysts and other metal catalystsmay be used in conjunction with titanium silicalite epoxidationcatalysts. Examples of such metal catalysts include but are not limitedto Ni, Pd, Pt, Cu, Ag, and Au. Noble metal catalysts are presentlypreferred.

[0016] The alkene which is epoxidized is a C₃ or higher alkene,preferably propylene, although the process is also useful with otheralkenes such as C₄₋₂₀ alkenes, more preferably C₄₋₈ alkenes, and yetmore preferably C₄ alkenes such as 1-butene and 2-butene. Cyclic alkenessuch as cyclohexene and cyclopentene are also useful, as are dienes andpolyenes, for example 1,3-butadiene. The epoxidation preferably takesplace continuously, for example in continuous stirred tank reactors(CSTR), tubular reactors, fixed bed and fluidized reactors, and thelike. In such processes, alkene and epoxidizing agent are fed to thereactor and contacted with the solid titanium silicalite catalyst. Thetemperature is adjusted to achieve a reasonable reaction rate withoutgeneration of byproduct types and amounts which would render sustainedoperation problematic. Reaction temperatures of 25° C. to 100° C. arepreferred, more preferably 30° C. to 80° C., and most preferably 40° C.to 70° C. Selection of the reaction temperature, reactor pressure,byproduct separation, and product purification are easily made by oneskilled in the art.

[0017] Most preferably, the process is an in situ process employinghydrogen, oxygen, and a catalyst suitable for forming hydrogen peroxidein situ. Since hydrogen and oxygen are “permanent gases,” unreactedportions may easily be separated from the reactor and recycled.Palladium is the preferred noble metal catalyst, but other noble metalswhich catalyze generation of hydrogen peroxide may be used as well, forexample Pt, Au, and Ag. The noble metal may be supported on silica,thermoplastic beads, or any other convenient support. However, suchsupports occupy reactor volume but do not catalyze olefin epoxidation.It has been found that the noble metal may be deposited onto titaniumsilicalite, and the catalyst then performs the double function of bothhydrogen peroxide generation and olefin epoxidation. Surprisingly,olefin epoxidation efficiency is maintained. Mixtures of untreatedtitanium silicalite and metal-treated titanium silicalite may also beadvantageously used.

[0018] The titanium silicalite catalysts useful in the present inventionare titanium silicalite single crystals and intergrowths having a meanparticle size greater than 2 μm. The term “intergrowth” should becontrasted with the prior use of “conglomerate” wherein sufficientbinder is added to form a shaped product, and wherein binder surroundssignificant portions of titanium silicalite crystals. The “intergrowths”of the present invention contain no binder to adhere crystals together.Most preferably, the crystals of the intergrowths are bound together bygrowth processes which yield an intertwined matrix of crystals withsubstantial integrity. An example of such intergrown crystals is shownin FIG. 1.

[0019] Single titanium silicalite crystals are generally flatrhombohedrons in shape. The minimum mean diameter (geometric) of singlecrystals across their major surfaces is 2 μm, but is preferably higher,i.e. 3-15 μm, more preferably 4-12 μm. At these large sizes, it ishighly surprising that useful epoxidation rates can be maintained. Largesingle crystals are generally flat rhombohedrons having an aspect ratio(length/thickness) of about 1 to 10, more preferably 1 to 6, and mostpreferably about 1 to 5. Small aspect ratios, i.e. 1-2, are mostpreferred. The thickness of the crystals is relatively small, i.e., inthe range of 0.3 to 5 μm, more preferably 0.4 to 3 μm, and mostpreferably 0.5 to 2 μm. An example of such crystals is shown in FIG. 2.

[0020] Use of intergrown titanium silicalite crystals for olefinepoxidation has not been disclosed. Intergrown crystals are comprisedsubstantially of titanium silicalite, with “primary” rhombohedralcrystals of relatively small size, i.e., preferably less than 5.0 μm insize across their major faces, and preferably less than 4 microns. Theintergrowths are grown by processes wherein a considerable amount ofintergrowth, “twinning,” etc., takes place, such that the intergrowthshave mean particle size (geometric mean in 3 dimensions) in excess of 2μm, more preferably in the range of 2-30 μm, and most preferably in therange of 4-20 μm. Reference may be had to FIG. 1, where the meanparticle size is about 4-5 μm. Surprisingly, it has been found that suchintergrowths have even higher epoxidation performance than singlecrystals of the same mean size.

[0021] Large titanium silicalite single crystals may be made byprocesses known in the art, for example those disclosed by U.S. Pat. No.5,401,486; EP 119 130; EP 543,247; and STUDIES IN SURFACE SCIENCE, V.84, p. 203-210. Small crystal titanium silicalite (i.e. 0.2 μm)synthesis is described in U.S. Pat. No. 4,410,501. Most preferably asynthetic method as disclosed herein is used. In the preparation oflarge single crystal titanium silicalites, a range of particle sizes aregenerally produced.

[0022] For preparation of intergrown catalyst particles, any methodwhich results in useful intergrowths having a particle (intergrowth)size greater than 2 μm may be used. It should be noted that such methodsof intergrowth preparation must not involve preparation of smallcrystals followed by calcination with a binder as is used to form“shaped” or “formed” conglomerated catalyst particles. Rather, thecrystal growth itself forms the intergrowth. Several examples ofmarkedly different intergrown “crystallites” are presented herein. Thesemethods are exemplary and not limiting.

[0023] In one method of titanium silicalite single crystal growth, ahydrolyzable precursor of titanium and a silica source, or hydrolyzableprecursor(s) containing both silicon and titanium, are hydrolyzed inwater, preferably in the presence of ammonia, hydrogen peroxide and atetraalkylammonium compound such as a tetraalkylammonium halide. Thefirst part of the preparation is conducted at 1 atm and mildtemperatures, between 5° C. and 85° C., where “gel” is made. The secondpart of the preparation, a hydrothermal crystallization, is generallyconducted in a sealed autoclave at elevated temperature, i.e. 150° C. to200° C., under autogenous pressure. At the end of the growth period, forexample 100 to 200 hours, the pressure is then released.

[0024] For the preparation of titanium silicalite intergrowths, crystalgrowth preferably occurs in a growth medium containing hydrolyzabletitanium, hydrolyzable silica, and tetrapropylammonium hydroxide. Thecrystallization is preferably conducted at 130° C. to 200° C., morepreferably at about 150° C. to 180° C. for an extended period,preferably for 1 to 8 days. The crystals are somewhat round (polyhedric)in appearance, and clearly exhibit numerous crystals and crystal faces.Scanning electron micrographs of a typical intergrowth is shown inFIG. 1. Preferred titanium and silica sources include alkyl- andalkoxy-functional siloxane/titanate copolymers. Such copolymers arecommercially available. By the term “hydrolyzable titanium/silicon”copolymer is meant a composition containing both silicon and titanium,with hydrolyzable functionality such that a titanium silicalite may beobtained by hydrolysis. Titanium and silicon-linked hydrolyzable groupsinclude, but are not limited to, alkoxy, hydrido, hydroxyl, halo, andlike groups. With respect to titanium, alkyl and aryl groups may bepresent as well.

[0025] It has further been discovered that the use of raw materialsources which are low in alkali metals and alkaline earth metals providelarge crystal titanium silicalite products with unexpectedly enhancedactivity. In particular, use of silica sources having less than 100 ppmsodium is highly desirable. Silica with even less sodium, for exampleabout 50 ppm or less, and with low aluminum and iron content is alsorecommended. Sources of such highly pure silica include fumed silicawhich is commercially available.

[0026] The titanium silicalite catalysts of the present invention arepreferably used in the previously described in situ process whereinhydrogen and oxygen rather than hydrogen peroxide are fed to the reactoras the source of oxygen for epoxidation. Under these conditions, thetitanium silicalite is altered to contain a noble metal, preferablypalladium, which may be applied to the titanium silicalite byconventional deposition processes. Any soluble palladium compound may beused in such deposition processes, or other methods of applying Pd maybe used. Tetraamine palladium dichloride and tetraamine palladiumdinitrate have both been used to successfully prepare palladium-treatedtitanium silicalite catalysts. Preferably, tetraamine palladiumdinitrate without an excess of ammonia is employed. The titaniumsilicalite may be treated, for example, with a solution of solublepalladium at 80° C. for 24 hours for the nitrate and 20° C. for 1 hourfor the chloride, followed by filtration and resuspension in deionizedwater. The product is then filtered and resuspended in deionized watertwice more. The palladium-treated product may be isolated, dried invacuum at 50° C. overnight, and calcined by heating in flowing 4 volumepercent oxygen in nitrogen to 110° C. (10° C./min), holding for 1 hour,and heating at 2° C./min to 150° C. followed by a 4 hour hold. Theweight percentage of palladium may range from 0.01 weight percent toabout 2 weight percent or higher, but is preferably 0.1 to about 0.8weight percent, more preferably 0.2 to 0.5 weight percent. Higherloadings of palladium can be accomplished by exposing apalladium-containing catalyst to further ion exchange from palladiumsolution followed by calcining, as described above. Further methods ofdepositing palladium and other catalytic metals may be found in the artof vehicular exhaust catalytic converters and other references dealingwith noble metal deposition. The methods described above are notlimiting.

[0027] Prior art catalysts have no commercial usefulness, as it isvirtually impossible to maintain continuous reactor operation with meanparticle sizes of 0.2 μm or less productivity due to clogging offilters. The present catalysts display an activity which is surprisinglyhigh when viewed in conjunction with the increased particle size. Eventhough the present process has not been optimized, epoxidation ratessimilar and in some cases superior to those of the prior art small sizetitanium silicalite crystals have been achieved. Processes employing thelarger catalysts of the subject invention can run for extended periodswithout shutdown. Thus, even for catalysts with lower production rates,the freedom from reactor down time makes these catalysts commerciallyviable.

[0028] Resistance to attrition is a necessary parameter for a commercialtitanium silicalite epoxidation catalyst. Attrition may be measured byperiodic sampling of solid catalyst from a reaction campaign, or may beassessed by an attrition test conducted in water or other suitablesolvent, and described below. The latter test has been shown toaccurately reflect attrition rate during epoxidation.

[0029] In the attrition test, a model reactor has a 3⅛ inch diameterI.D. and has a 2 inch diameter Rushton turbine with 6 vanes, rotating at650 RPM. The baffle cage has 4 strips, each){fraction (5/16)} inch wide.50 μm of large crystal TS-1 are charged with 500 ml of deionized waterand agitated at 20° C. No chemistry is conducted during the test. Thetitanium silicalite, when present as single crystals, is originally inthe form of plates, normally with flat or slightly convex ends andstraight sides. For example, in an actual test, measurements madedirectly from electron microscope images showed mean dimensions of10.2×7.63×1.87 microns, approximately in accordance with the values froman automated laser-based technique. Samples are subjected to electronmicroscopy and particle size distribution measurement by laserdispersion, although any method of determining particle size anddimensions may be used. The volume-based median diameter (d_(vol, 50%))and the number-based median diameter (d_(0, 50%)) may be extracted fromthe size distribution data, and show a slow disintegration over time.The electron micrographs show a steady increase in the proportion offines, mainly chips from the corners and the edges of the titaniumsilicalite platelets.

[0030] The volume and number-based median particle sizes may be plottedas the logarithms of their values against time in days, assuming thatthe size attrition is a first order process. A linear least squares fityields the following equations tracking size attrition for the exampledescribed above: d_(vol,50%) (microns) = 10^(−0 0009t+0 9799) t = timein days Equivalent to −0.21%/day d_(n,50%) (microns) =10^(−0 0005t+0 8974) t = time in days Equivalent to −0.12%/day

[0031] These relationships generate plots which are properly of negativeslope and of correct relative magnitude in the range of the data butintersect at high values of time. The particle size data at 0 hours wereexcluded from these curve fits because the first 24 hours of the testcause disintegration of loosely associated crystallites, whichinterferes with the data. Using these equations, the particle sizes at180 and 365 days are projected to be as follows: d_(vol, 50%) of 6.58and 4.48 microns and d_(n, 50%) of 6.42 and 5.19 microns. It should benoted that conglomerates prepared by spray-drying 0.2 μm titaniumsilicalite crystals with kaolin or alumina binders exhibited asubstantially higher attrition rate, expressed as the rate of decline inthe median particle diameter based on volume, averaging 18.6%/day, fartoo high to be useful. The catalyst particles should have an attritionrate no higher than 2% (loss) per day, preferably less than 1% per day,and more preferably 0.5% or less per day.

[0032] The chemical efficiency of the various catalysts herein isassessed initially by a screening test in batch mode. The “screeningtest” is performed in a high pressure stainless steel autoclave, usinghydrogen peroxide as the epoxidizing agent. The autoclave is chargedwith 40 g of 84 wt. % methanol, 4.8% hydrogen peroxide, balance water,and 0.15 g titanium silicalite-containing catalyst, the catalystpreferably being substantially all titanium silicalite. The reactor issealed and heated to 50° C. and 19 g propylene injected. Agitation isprovided by means of a stir bar, revolving at 600 RPM (10 s⁻¹). After0.5 h, the reactor is shock chilled to stop the reaction, and residualpropylene degassed into a gas bag. The propylene is weighed andanalyzed, as is the aqueous phase remaining in the reactor. The hydrogenperoxide conversion efficiency, propylene oxide produced (“PO”) andpropylene oxide equivalents produced (“POE”) are reported. By propyleneoxide equivalents is meant propylene oxide and derivatives, i.e.,propylene glycol, acetol, 1-methoxy-2-propanol, 2-methoxy-1-propanol,dipropylene glycol, tripropylene glycol, methoxydipropylene glycol, andmethoxytripropylene glycol, among others. The selectivities are reportedin percent as (mol PO/mol POE)×100%, measuring the relative extent of POring opening, and (mol POE/mol propylene consumed)×100%, measuring theselectivity of propylene conversion to POE. Another importantmeasurement of selectivity is (mol POE/mol hydrogen peroxideconsumed)×100% which measures the selectivity of hydrogen peroxideepoxidation of propylene to POE. In these experiments, the controlcatalyst for purposes of comparison is a titanium silicalite having aparticle size of 0.2 μm and a Ti content of 1.1 wt. %.

[0033] In a preferred commercial olefin epoxidation process, thetitanium silicalite epoxidation catalyst is slurried in a reactionmixture liquid phase which may preferably comprise water, loweralcohols, alkylalcohol ethers, ketones, and the like. The catalyst ispreferably present in as large an amount which can be effectivelymaintained as a slurry, i.e., without undue sedimentation to a staticbed. The reactor is preferably a draft tube reactor, as disclosed inU.S. Pat. No. 5,972,661, however other reactor configurations arepossible, including tubular reactors and slurry reactors. Alternatively,the reactor may constitute a fixed bed of catalyst particles.

[0034] The reactant feed streams comprise, in addition to olefin,hydrogen peroxide and make-up solvent in the case of non-in-situreactors, and hydrogen, oxygen, and make-up solvent in the case ofin-situ reactors. Other reaction moderators, accelerators, buffers, etc.may be added as necessary. For example, an alkali metal hydrogencarbonate feed stream may be added. Triammonium phosphate, diammoniumphosphate, monoammonium phosphate and mixtures thereof may be added as afeed stream. When hydrogen peroxide is employed in a non-in-situprocess, feed streams of oxygen and/or hydrogen may be introduced. Inin-situ processes, likewise, a peroxide feed stream may be additionallyintroduced.

[0035] The reactor is maintained at a suitable temperature, as describedpreviously, and a product take-off stream, containing alkylene oxideproduct, alkylene oxide equivalents, solvent, catalyst and catalystfines, etc., is continuously removed from the reactor. From this productstream, large size catalyst particles, i.e. those having a size of >1μm, preferably greater than 2 μm, may be recycled to the reactor, havingbeen separated by conventional separating techniques, while catalystfines, particularly those having a particle size <0.5 μm, morepreferably <0.2 μm, are discarded or used as raw material for additionalcatalyst synthesis. In some processes, the product stream will containsubstantially no catalyst particles, or only catalyst “fines,” the bulkof the catalyst particles remaining in the reactor.

[0036] Alkylene oxide product is separated by distillation from theremaining non-solid components of the product stream, and reactordispersion medium/solvent is advantageously recycled, any loss beingmade up of “make-up” solvent.

[0037] In the case of in-situ reactions, it is preferable that thereaction take place at relatively high pressure, i.e., at 50 to 1500psig, preferably 100 to 500 psig, and most preferably 100-200 psig andthat substantially pure hydrogen and oxygen feeds be introduced into thereactor. While introduction of nitrogen or other inert gas is notprecluded, obtaining effective concentration of hydrogen and oxygen at agiven reactor pressure is rendered more problematic.

[0038] The gas oxygen and hydrogen partial pressures are adjusted topreferably product a gas composition below the explosion limit. Oxygenpartial pressure is preferably 3 to 50 psig (122 to 446 kPa), morepreferably 5 to 30 psig (135 to 308 kPa), and most preferably 5 to 20psig (135 to 239 kPa), while the hydrogen partial pressure is preferably2 to 20 psig (115 to 239 kPa), more preferably 2 to 10 psig (115 to 170kPa), and most preferably 3-8 psig (122 to 156 kPa). Hydrogen and oxygennot reacted are preferably burned as fuel, rather than beingrecompressed and reused. However, it is also possible to recycle thesecomponents.

EXAMPLE 1

[0039] Titanium Silicalite Large Crystal Synthesis, Method 1

[0040] To a 3-neck flask is charged 51.06 g distilled water which isthen cooled with agitation to 5° C. by means of an ice/water bath. Anitrogen blanket is established with an N₂ feed rate of 150 cm³/m. Tothe cooled water, 4.4955 g titanium (IV) isopropoxide (98%, Strem93-2216) is added, with vigorous stirring, following which 9.102 g 30%hydrogen peroxide is added to the flask over 15 min with very vigorousstirring. The flask is stirred for an additional 10 minutes at 5° C. Thecolor of the solution turns yellow upon addition of the hydrogenperoxide, then gold and finally orange. To 254.237 μm of aqueous ammoniais added 45.763 g deionized water to form a 25 wt. % aqueous ammoniasolution. The flask is removed from the ice bath, and 250.88 g of the25% aqueous ammonia is added with continuous stirring. The solutionbecomes pale green with some white precipitate. The contents are stirredfor 10 minutes, then heated to 80° C. and stirred at this temperaturefor 3 hours. The heat source is removed, and stirring continuedovernight with nitrogen purge at 125 cm³/m. The flask is weighed, andthe remainder of the 25% aqueous ammonia added. The contents are stirredat high speed for 80 minutes.

[0041] To the flask, a mixture of 16.432 g tetrapropylammonium bromidesolution in 49.75 g distilled water is added rapidly with sustainedagitation. To the contents, 23.3 μg Aerosil® 380 silica (Degussa) isthen added, and mixed well.

[0042] The entire contents of the flask are transferred to a clean,Teflon-lined, unstirred 1000 ml autoclave which is flushed with nitrogenfor 3-5 minutes at 100-150 cm³/min to displace oxygen from the headspace. Any positive pressure is released, and the autoclave sealed. Theautoclave is heated to 185° C. and stirred at autogenous pressure forapproximately 8 days. The autoclave is slowly cooled to roomtemperature, and the solid product isolated as a wet filter cake on anominal 5 μm filter, redispersed in 300 ml of 80° C. distilled water,agitated vigorously, and again filtered. This distilled water wash isrepeated twice more, following which the catalyst is dried at 60° C.under vacuum overnight. The material is calcined for 4 hours at 110° C.in a Ney oven, followed by calcining at 550° C. for 6 hours in air.Prior to use, the subject invention catalysts were slurried in water andoptionally filtered on 0.45 μm, 0.8 μm, or 5.0 μm filters, retaining thefiltercake (and thus the larger particles).

[0043] In the general procedure set forth heretofore, the weightpercentage of Ti may be adjusted by increasing or decreasing the amountof titanium (IV) isopropoxide initially added to the flask. Thepractical limit of Ti incorporation into the zeolite framework is circa2.0 weight percent, according to the literature. Use of higher levels oftitanium are said to result in anatase formation, which is stated toreduce yield in epoxidation with small (0.2 μm) crystals. Large crystalshave been prepared with titanium contents of from about 1.3 to about 4weight percent. It should be noted that the Teflon liner of theautoclave should be scrupulously cleaned between catalyst preparation,or a new liner installed.

COMPARATIVE EXAMPLE C1

[0044] A titanium silicalite catalyst having a mean particle size of 0.2μm is prepared by methods of the prior art employingtetraethylorthosilicate as the silica source. See, e.g., U.S. Pat. No.4,410,501, Example 1.

EXAMPLES 2-7 AND COMPARATIVE EXAMPLE C2

[0045] Large size titanium silicalites were prepared by the generalmethod discussed previously and compared to a prior art titaniumsilicalite catalyst C1 exhibiting typical epoxidation activity andcontaining 1.1 wt. % titanium, all of which is believed to beincorporated as titanium silicalite in a zeolitic structure. The variouscatalysts were tested in the screening test described previously. Theresults are presented in Tables 1 and 2 together with the analytical andother data believed to be relevant. Complete elemental analyses were notperformed for all catalysts. Example 7 consisted of large crystals fromwhich fines were removed by filtration and tested for activity asComparative Example C2. TABLE 1 Large Crystal TS-1 Syntheses andEpoxidation Catalysis Catalyst C1 1 2 3 4 Theo. Ti (wt %) NA 1.38 2.762.76 1.38 Filter None 0.45 0.8 micron 0.8 micron 5 micron micron Elem.an. (wt %) Al <0.01 0.028 NS 0.0465 0.042 C 0.39 <0.1 0.39 0.1 Cl <0.01<0.001 <0.001 <0.001 Cu <0.001 0.0055 <0.001 <0.001 Fe <0.001 0.0130.015 0.014 <0.001 H 0.11 <0.1 <0.1 <0.1 N <0.1 <0.1 <0.1 <0.1 K <0.001<0.001 0.001 <0.001 Na <0.01 0.018 NA 0.145 0.052 Si 45 46 44 44.3 46 Ti1.1 1.21 2.68 2.64 1.24 Mean Length, μm 0.2 12 8.5 6.7 5.8 Mean Width,μm 0.2 5 3.9 2.4 1.7 Mean Thickness, 0.2 1.7 0.87 0.78 0.52 μm N₂ sur.area NA 287 NA 316 371 (m²/g) Estimated Ti in 100 40 48 41 52 TS-1framework relative to Ti (%)¹ Estimated Ti in 1.1 0.478 1.29 1.09 0.644TS-1 framework (wt %)¹ H₂O₂ conv (%) 43 17.1 38.3 33.7 24.6 PO (mmole)18.50 8.647 15.35 14.79 10.45 POE (mmole) 19.43 9.116 18.21 16.78 12.03POE selectivity 75.62 85.87 76.78 79.19 79.54 relative to H₂O₂ (%)#shown by diffuse reflectance ultra violet spectroscopy and Xrayspectroscopy to contain all the Ti in a zeolite framework. This methodallows the Ti in the TS-1 framework of other samples to be determinedand the proportion of that relative to the total Ti may be computed fromthe elemental analysis.

[0046] TABLE 2 Large Crystal TS-1 Syntheses and Epoxidation CatalysisCatalyst C1 5 6 C2 7 Theo. Ti NA 1.38 1.38 4.04 4.04 (wt %) Filter None5 micron 5 micron 5 micron 5 micron Elem. an. (wt %) Al <0.01 0.0530.068 NA NA C 0.39 Cl <0.01 Cu <0.001 Fe <0.001 0.012 0.014 0.011 NA H0.11 N <0.1 K <0.001 Na <0.01 0.054 0.065 NA NA Si 45 46 45 44 NA Ti 1.11.14 1.25 <0.001 NA Mean Length, 0.2 8.5 8.1 10.8 NA μm Mean Width, 0.22.6 1.6 2.5 NA μm Mean Thick- 0.2 0.72 0.62 0.81 NA ness, μm N₂ sur.area NA 351 NA 305 NA (m²/g) Estimated Ti 100 64 46 21 NA in TS-1framework relative to Ti (%)¹ Estimated Ti 1.1 0.729 NA 0.639 NA in TS-1framework (wt %)¹ H₂O₂ conv (%) 43 21.34 19.98 7.09 32.08 PO (mmole)18.50 8.00 7.91 10.66 14.20 POE (mmole) 19.43 9.76 9.38 11.85 16.69 POEselectivity 75.62 74.66 76.6 NA 85.10 relative to H₂O₂ (%)

[0047] Tables 1 and 2 indicate that the large size titanium silicalitecatalysts have slightly lower activity than the very small prior artcatalysts. However, the decrease in activity is nowhere near thatexpected in view of the much larger catalyst particle size. Examples 2and 3, for instance, exhibit an average loss in hydrogen peroxideconversion of only about 16%, while selectivity to propylene oxideactually increased somewhat. It is also surprising that the large sizetitanium silicalite catalysts showed greater activity when fines areincreasingly removed. For example, the large titanium silicalitescollected on 0.8 and 5 μm filters showed greater activity than thosecollected on 0.45 μm filters. One would expect the catalysts containingmore small particles to exhibit a higher H₂O₂ conversion rate. However,this is not the case. In Example 7 and Comparative Example C2, theactivity of the retains (large crystals) are compared with the activityof the crystals which pass through a 5 μm filter. The former gave anH₂O₂ conversion of 32.08% as compared to 7.09% for the fines, theopposite of what one would expect. The catalyst of Example 6 wasslurried in 98% sulfuric acid, washed, dried at 110° C., and calcined.Prior to this treatment, the catalyst had shown relatively low activity(7.1% H₂O₂ conversion). Washing with sulfuric acid is one way ofincreasing catalytic activity. The titanium silicalite crystals wereprepared by the general method heretofore described, employing LudoxAS40 colloidal silica (DuPont).

EXAMPLES 8-10

[0048] A variety of titanium silicalite catalysts were prepared from asilica source having a low sodium content. Fumed silica (Aerosil® 380,Degussa) was employed as the silica source. In addition to low sodiumcontent, lower iron and aluminum content is present as compared to theLudox® AS40 colloidal silica employed in the examples of Tables 1 and 2.The sodium content of Aerosil® 380 is less than 50 ppm as compared to1300 ppm of the colloidal silica. Trials of a variety of titaniumsilicalites prepared using a low sodium silica source are compared witha conventional small size titanium silicalite catalyst of the prior art,and subject invention large size titanium silicalite catalysts preparedfrom a “high” sodium silica source. The relevant physical and chemicalproperties and catalytic activity are presented in Table 3 below. TABLE3 Large Crystal TS-1 Synthesis and Epoxidation Catalysts Catalyst C1 4 57 8 9 10 SiO₂ source Low Low Na Low Na Na Theo. Ti (wt %) NA 1.38 1.38 4.04 4.04 3.03 2.02 Filter None 5 μm 5 μm 5 μm 5 μm 5 μm 5 μm Elem. an.(wt %) Al <0.01 0.042 0.053 NA 0.0051 0.0077 <0.002 C 0.39 Cl <0.01 Cu<0.001 Fe <0.001 <0.001 0.012 NA 0.0035 0.0034 0.005 H 0.11 N <0.1 K<0.001 Na <0.01 0.052 0.054 NA <0.005 <0.005 0.005 Si 45 46 46 NA 43 4445 Ti 1.1 1.24 1.14 NA 3.89 2.65 1.95 Mean Length, 0.2 5.8 8.5 NA 9.138.06 8.32 μm Mean Width, μm 0.2 1.7 2.6 NA 5.27 3.93 2.65 MeanThickness, 0.2 0.52 0.72 NA 1.53 0.811 0.794 μm N₂ sur. area NA 371 351NA 305 305 NA (m²/g) Estimated Ti in 100 52 64 NA 34 57 72 TS-1framework relative to Ti (%) Estimated Ti in 1.1 0.644 0.729 NA 1.321.514 1.396 TS-1 framework (wt %) H₂O₂ conv (%) 43 24.6 21.34 32.0832.52 39.60 34.10 PO (mmole) 18.50 10.45 8.00 14.20 14.69 21.21 16.95POE (mmole) 19.43 12.03 9.76 16.69 16.56 23.72 18.75 POE selectivity75.62 79.54 74.66 85.10 77.44 97.95 88.88 relative to H₂O₂ (%)

[0049] The results in Table 3 indicate that by selecting a low sodiumsilica source, both H₂O₂ conversion efficiency and selectivity are highas compared to otherwise similar catalysts prepared from higher sodiumcontent silica. Results at an intermediate Ti level (Example 9) exhibitnearly the same H₂O₂ conversion efficiency as the small titaniumsilicalite catalysts of the prior art (>90% relative to 0.2 μmcrystals), while the propylene oxide equivalents selectively relative tohydrogen peroxide is truly excellent (ca. 98%). The amount of Tiemployed (ca. 4 wt. %) is higher than can be incorporated into a TS-1structure, contrary to the teachings of the prior art which indicatethat non-framework Ti is detrimental.

[0050] Titanium Silicalite Crystalline Intergrowth Syntheses, Method 2

[0051] For preparation of intergrowths, tetrapropylammonium hydroxide ormixtures of tetralkylammonium hydroxide and tetraalkylammonium halideare used. Silica and titanium sources may be the same as for singlecrystal growth, but preferably used in Method 2 are siloxane/titanatecopolymers such as alkoxysilane/alkyltitanate copolymers. One suchcopolymer is Gelest PSI TI-019, a diethoxysilane and ethyltitanatecopolymer containing 19.4 wt. % silicon and 2.2 wt. % Ti. In general, atetralkylammonium salt and a base are required. Suitable bases includeorganic amines, ammonia, and tetralkylammonium hydroxide.

EXAMPLE 11

[0052] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 6.8 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-109, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 10 g of 40 wt % aqueous tetrapropylammonium hydroxide (Alfa)and 25 g water. The mixture was stirred and heated to 80° C. to removeethanol by distillation. The volume was reconstituted with additionalwater and the mixture was introduced into a shaker bomb (autoclave)heated at 150° C. for 7 days. The solid product, 2.2 g of a whitepowder, was analyzed and found to contain 37 wt % Si, 1.1 wt % Ti, 9.2wt % C and 0.99 wt % N. The x-ray diffraction pattern was consistentwith pure titanium silicalite (TS-1). Scanning electron microscopy ofthe product indicated that relatively large (ca. 6-7 micron) crystallineagglomerates were produced, consisting of highly intergrown crystals.

EXAMPLE 12

[0053] A crystalline titanium silicate ETS-10 (Englehard) containing66.1 wt % SiO₂, 10.0 wt % Na₂O, and 4.8 wt % K₂O was ion-exchanged threetimes with 1M NH₄NO₃ at 80° C. To 10 g 40% tetrapropylammonium hydroxide(Alfa) in 25 g water, was added 5.0 g of the ion-exchanged product fromabove. The mixture was introduced into a shaker bomb maintained at 180°C. for 5 days. The recovered product was pure titanium silicalite (TS-1)by x-ray diffraction, and analyzed for 39 wt % Si and 1.7 wt % Ti. SEMshowed crystalline agglomerates, in the size of ca. 3 microns, with ahigh degree of intergrowth.

EXAMPLE 13

[0054] A mixture was prepared containing 7.14 g TEOS (tetraethylorthosilicate), 7.07 g titanium-(triethanolaminato) isopropoxide (80% inisopropyl alcohol), 21 g water, 7.39 g 40 wt % tetrapropylammoniumhydroxide (Alfa), and 0.43 g HZSM-5 (CBV-10002 from PQ, with Si/A1=255).The mixture was heated in a shaker bomb at 150° C. for 7 days. 2.38 g ofa white solid was recovered, and shown to be pure titanium silicalite(TS-1) by XRD. After calcination in air at 550° C., the solid analyzedfor 41 wt % Si and 1.2 wt % Ti. SEM indicated the presence ofcrystalline intergrowths, 5-10 microns in size.

EXAMPLE 14

[0055] A mixture of 3.97 g of an amorphous titanosilicate (containing7.0 wt % Ti and 38 wt % Si), 10.0 g 40% tetrapropylammonium hydroxide,23.9 g water, and 0.4 g HZSM-5 (CBV-10002 from PG, with Si/A1-255) washeated in a shaker bomb at 180° C. for 4 days. 3.97 g of a white solidwas recovered and shown to be pure TS-1 by XRD. After calcination in airat 550° C., the product analyzed for 1.6 wt % Ti and 41 wt % Si. SEMindicated the presence of crystalline intergrowths, greater than 5microns in size.

EXAMPLE 15

[0056] An intergrowth crystalline titanium silicalite (TS-1) catalystwas prepared by mixing together 6.99 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 1.97 g tetrapropylammonium bromide, 0.31 g calcined TS-1 (1.45wt % Ti), 1.02 g 40 wt % aqueous tetrapropylammonium hydroxide (fromAlfa), and 28 g water. The mixture was heated in a shaker bomb at 150°C. for 7 days, and a solid product, 3.56 g, was recovered. The x-raydiffraction pattern was consistent with pure titanium silicalite.Scanning electron microscopy of the product indicated that relativelylarge (ca. 6-8 micron) crystalline agglomerates were produced,consisting of highly intergrown crystals.

EXAMPLE 16

[0057] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 5.99 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc. containing 19.4 wt % Si and 2.2 wt %Ti), which was preheated at 75° C. for 2 hours with 0.33 g of a calcinedTS-1 containing 1.45 wt % Ti, 10.07 g 40 wt % aqueoustetrapropylammonium hydroxide (from Alfa), and 20 g water. The mixturewas heated in a shaker bomb at 200° C. for 2 days, and a solid product,3.1 g, was recovered. The x-ray diffraction pattern was consistent withpure titanium silicalite (TS-1). After calcination at 550° C., theproduct analyzed for 4.0 wt % Ti and 39 wt % Si. Scanning electronmicroscopy of the product indicated that relatively large crystallineagglomerates were produced, consisting of highly intergrown crystals.

EXAMPLE 17

[0058] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 10.03 g of a diethoxysilane-ethyltitanatecopolymer (PS9150, United Chemical Technology, Inc., containing 44-47 wt% SiO₂ and TiO₂ with Si/Ti—12-13), which was preheated under flowingnitrogen at 80° C. for one hour with 0.33 g of a calcined TS-1containing 1.45 wt % Ti, 10.04 g 40 wt % aqueous tetrapropylammoniumhydroxide (from Alfa), and 20 g water. The mixture was heated at 550°C., the product analyzed for 3.5 wt % Ti and 29 wt % Si. Scanningelectron microscopy of the product indicated that relatively largecrystalline agglomerates were produced, consisting of highly intergrowncrystals.

EXAMPLE 18

[0059] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 7.06 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc. containing 19.4 wt % Si and 2.2 wt %Ti), which was preheated at 75° C. for 2 hours with 0.35 g of a calcinedTS-1 containing 1.45 wt % Ti, 10.52 g 40 wt % aqueoustetrapropylammonium hydroxide (from Alfa), and 20 g water. The mixturewas heated in a shaker bomb at 180° C. for 3 days, and a solid product,3.24 g, was recovered. The x-ray diffraction pattern was consistent withpure titanium silicalite (TS-1). After calcination at 550° C., theproduct analyzed for 1.3 wt % Ti and 41 wt % Si. Scanning electronmicroscopy of the product indicated that relatively large crystallineagglomerates were produced, consisting of highly intergrown crystals.

EXAMPLE 19

[0060] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 13.6 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 2.7 g tetrapropylammonium bromide, 5 g 40 wt % aqueoustetrapropylammonium hydroxide (from Alfa) and 36 g water. The mixturewas stirred and heated to 80° C. to remove ethanol by distillation. Thevolume was reconstituted with additional water and the mixture wasintroduced into a shaker bomb (autoclave) heated at 175° C. for 5 days.The solid product, 5.07 g of a white powder, was analyzed and found tocontain 38 wt % Si, 2.2 wt % Ti, 9.0 wt % C and 0.92 wt % N. The x-raydiffraction pattern was consistent with pure titanium silicalite (TS-1).Scanning electron microscopy of the product indicated that relativelylarge crystalline agglomerates were produced, consisting of highlyintergrown crystals.

EXAMPLE 20

[0061] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 19.98 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 1.05 g HZSM-5 (from PQ, CBV-10002, Si/A1=255). The mixture washeated at 70° C. for 2 hours, then kept overnight at room temperature.7.37 g of this mixture was then added to 10.0 g 40% tetrapropylammoniumhydroxide (from Alfa) in 20.1 g water. The mixture was introduced into ashaker bomb (autoclave) and heated at 175° C. for 5 days. The solidproduct, 4.14 g of a white powder, exhibited the x-ray diffractionpattern of pure titanium silicalite (TS-1). After calcination at 550°C., the product analyzed for 1.3 wt % Ti and 44 wt % Si. Scanningelectron microscopy of the product indicated that relatively largecrystalline agglomerates were produced, consisting of highly intergrowncrystals.

EXAMPLE 21

[0062] An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 6.86 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with a solution of 2.0 g tetrapropylammonium bromide and 20 gconcentrated ammonium hydroxide in 20 g water. The mixture wasintroduced into a shaker bomb (autoclave) and heated at 175° C. for 7days. The solid product, 2.3 g of a white powder, exhibited the x-raydiffraction pattern of pure titanium silicalite (TS-1). Aftercalcination at 550° C., the product analyzed for 4.1 wt % Ti and 42 wt %Si. Scanning electron microscopy of the product indicated that extremelylarge crystalline agglomerates (greater than 20 microns in size) wereproduced, consisting of highly intergrown crystals.

[0063] Catalysis:

[0064] Propylene Epoxidation with Pre-Formed Hydrogen Peroxide

[0065] Intergrown titanium silicalite catalysts were evaluated forepoxidation activity by the standard screening test described earlier.The results are shown below: Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Catalyst 1314 15 16 17 18 19 20 H₂O₂ 46.8 31.0 49.4 54.3 58.9 60.0 45.9 48.8Conversion (%) PO (mmol) 25.2 18.7 26.2 30.4 34.0 34.2 25.3 27.2 POE(mmol) 29.3 20.3 28.9 33.3 37.7 35.6 26.5 29.0

[0066] The results indicate even higher activity than that of many 0.2μm single crystals of the prior art, which is highly surprising in viewof the limited surface area of the intergrown crystals as compared to0.2 μm single crystals.

[0067] General Method, Continuous In Situ Epoxidation

[0068] For continuous in situ olefin epoxidation, a Pd-treated catalystis slurried at 100 g catalyst/liter in 75/25 (w/w) methanol/water.Reactant feeds consist of liquid propylene and a gas mixture comprisingO₂, N₂, and H₂. A cylindrical stainless steel pressure reactor is used,with a 2 inch diameter Rushton turbine impeller providing agitation. Thereactor has an essentially flat bottom surface, with about ¼ inch radiusconcave peripheral chamfers. The impeller is located above the upperactive face of a filter in the form of a ring of sintered 316 stainlesssteel. The filtered fluid passes into a channel which is machined in thefilter body and which passes around the entire ring.

[0069] The hydrogen feed is supplied through a port in the base of thevessel. The liquid propylene feed and previously mixed methanol andwater solvent feed are combined externally to the reactor and fedthrough a dip tube to a point above the base of the vessel. Each gasfeed is monitored via a gas mass flow meter, while liquid feeds aremonitored via liquid mass flow meters. The exit gas and filtered exitliquid are analyzed every 2 hours by in-line GC.

[0070] The reactor liquid level is controlled by measuring thedifference in pressure between the oxygen feed gas dip tube, whichterminates close to the base of the vessel, and the head space of thereactor. The differential pressure cell has a range of 20 inches watergauge. Deviations in the level from the controller set point (normally4.0 to 5.0 inches) result in corrective action via the flow rate controlvalve in the filtered liquid exit line.

[0071] The reactor is usually run at 500 psig and 45° C. or 60° C. Thereis no draught tube in the reactor and it is intermediate between lab andpilot plant scales. Several in situ runs employing Pd-treated titaniumsilicalite catalyst were made.

EXAMPLE 22

[0072] The results are presented in Table 5. In Tables 5 and 6,abbreviations such as SPPO, SOPO, etc., refer to selectivity (S) basedon propylene feed (P), hydrogen feed (H) or oxygen feed (0) with respectto the particular product, i.e. propylene oxide (PO), propylene oxideequivalents (POE), ring opened products (RO:POE minus PO), propane,water, or carbon dioxide. Thus, SPPO is the selectivity (mol/mol) ofpropylene conversion to propylene oxide, while SOPO is the selectivityof oxygen conversion to propylene oxide. TABLE 5 Continuous ReactionUsing Pd on Large TS-1 Crystals (Example 22) 2 3 1 Hydrogen OverallAfter Break-in Feed Run, Maximum POE Best Rate After Time PeriodDesignation Overall Performance Reduced Break-in Start time (hr) 25.98137.97 25.98 End time (hr) 76.00 165.95 165.95 Duration (hr) 50.02 27.98139.97 Feed ratios Propylene/hydrogen 1.86 2.14 1.92 Oxygen/hydrogen2.00 2.30 2.07 Exit partial pressure (psi) Propylene 7.42 12.00 9.59Oxygen 18.63 19.45 18.90 Hydrogen 2.25 3.37 3.06 Conversion (%)Propylene 20.18 9.71 14.40 Oxygen 15.00 16.33 17.06 Hydrogen 76.12 62.8168.84 Rate PO productivity 0.017 0.020 0.019 (gmPO/gcathr) ROproductivity 0.031 0.022 0.028 (gmPO/gcathr) POE productivity 0.0470.042 0.045 (gmPO/gcathr) POE productivity 4.7 4.2 4.5 (gmPO/literslurry hr) PO/POE (%) 35.00 48.02 42.66 Propylene Selectivity SPPO (%)30.34 39.78 35.75 SPRO (%) 56.93 43.10 48.68 SPPOE (%) 87.28 82.89 84.43SPPropane (%) 11.76 16.56 14.83 SPCO₂ (%) 0.97 0.55 0.73 OxygenSelectivity SOPO (%) 14.45 22.69 18.52 SORO (%) 28.99 24.73 25.05 SOPOE(%) 41.45 47.42 43.57 SOH₂O (%) 56.66 51.17 54.84 SOCO₂ (%) 1.89 1.401.59 Hydrogen Selectivity SHPOE (%) 31.05 25.93 26.69 SHPropane (%) 3.186.27 4.91 SHH₂O (%) 65.77 67.80 68.40

EXAMPLES 23-26

[0073] Additional continuous runs have been conducted employing furthercatalysts. The results are presented in Table 6 below. Example 26employed a 1:1 mixture of two palladium-treated catalysts, whose basecatalysts, prior to Pd-treating, were prepared in the same manner andwith the same reactants and reactant ratios as the base catalyst ofExample 24, i.e. Example 9 of the subject invention. The respective basecatalyst particles had mean dimensions of 9.69×3.65×1.038 μm and5.91×2.66×0.595 μm, respectively. Analysis revealed 3.08 and 3.18 weightpercent titanium as compared to 2.65 weight percent titanium of the basecatalysts of claim 26. Screening test results showed 35.8 and 40.69 H₂O₂percent conversion, and 19.87 and 22.61 mmol POE. POE selectivity was91.42 and 90.89, respectively. The Pd-treated catalysts of Example 26were treated with Pd(NH₃)₄ (NO₃)₂ and calcined as previously disclosed.Pd weight percent was 0.49. TABLE 6 Example 23 24 25 26 Large TS-1 PrepExample 8 Example 9 — See text Mass cat (gm) 16.14 15.2 40.07 37.22 VolSlurry (ml) 400 400 400 400 Cat conc 4.035 3.8 10.02 9.305 (gm/100 ml)Hours on Stream (hr) 235 91.23 166 102 Press (psig) 500 500 500 500 Temp(C.) 60 60 60 60 Agit (RPM) 750 750 750 750 Feed 90 methanol 75 methanol75 methanol 75 methanol Composition (wt %) 10 water 25 water 25 water 25water Ammonium Bicarbonate Feed Zero 71 150 (0-46.5 hr) 2000 (0-48 hr)(ppm in liquid feed) 285 (46.5-166 hr) 1000 (48-102 hr) Peak POE(gmPO/gmcat hr) 0.07 0.15 0.055 0.32 At POE peak: 84 SPPOE (%) 93 93 8860 SOPOE (%) 10 58 46 35 SHPOE (%) 5 39 28 Mean POE 0.03 0.107 0.045 NA(gmPO/gmcat hr) Mean: NA SPPOE (%) 10 91 84 NA SOPOE (%) 5 36 44 NASHPOE (%) 3 22 27

[0074] The results indicate that significant in situ epoxidation hasoccurred. It should be noted that the results are based on a relativelysmall scale reactor, using considerable nitrogen in the oxygen feed. Ina commercial reactor, both the reactor pressure as well as the partialpressure of oxygen are expected to be changed to higher values, i.e.,using a pure oxygen feed.

EXAMPLE 27

[0075] In-Situ Propylene Epoxidation with Hydrogen and Oxygen

[0076] To 1 g of intergrown catalyst of Eample 11 dispersed in 87 gmethanol was added 0.0181 g palladium tetraamine dibromide dissolved in20 g water. This mixture was stirred at room temperature for 2 hours.The temperature was then raised to 45° C. and, at atmospheric pressure,flows of 20% H₂/80% propylene at 25 cm³/min and 5% O₂/0.6% CH₄/94.4% N₂at 88 cm³/min were introduced into the stirred slurry. Exit gas flowswere analyzed by on line gas chromatography. At 30 hours on stream, theexit gas contained greater than 1600 ppm propylene oxide.

[0077] While embodiments of the invention have been illustrated anddescribed, it is not intended that these embodiments illustrate anddescribe all possible forms of the invention. Rather, the words used inthe specification are words of description rather than limitation, andit is understood that various changes may be made without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. A process for the epoxidation of olefins, saidprocess comprising: a) providing a reactor containing a titaniumsilicalite epoxidation catalyst, said titanium silicalite being in theform of crystals or crystal intergrowths, said crystals or crystalintergrowths having a mean particle size of greater than 2 μm; b)supplying olefin to said reactor; c) supplying at least one of hydrogenperoxide or both hydrogen and oxygen to said reactor, whereby at least aportion of said olefin is epoxidized to an alkylene oxide; and d)isolating said olefin oxide, wherein when hydrogen and oxygen aresupplied to the reactor, the reactor further contains a metal catalyst.2. The process of claim 1, wherein said olefin is an a-olefin.
 3. Theprocess of claim 1, wherein said olefin is propylene.
 4. The process ofclaim 1, wherein at least a portion of said titanium silicaliteepoxidation catalyst is treated to contain a noble metal which iseffective to catalyze formation of hydrogen peroxide from hydrogen andoxygen.
 5. The process of claim 2, wherein said noble metal is selectedfrom the group consisting of palladium, gold, platinum, and mixturesthereof.
 6. The process of claim 4, wherein a noble metal treatedparticulate other than a titanium silicalite crystal or crystalintergrowth is further provided to said reactor.
 7. The process of claim1, wherein said titanium silicalite catalyst comprises intergrowths oftitanium silicalite crystals.
 8. The process of claim 1, wherein saidtitanium silicalite is prepared from a hydrolyzable silica sourcecontaining less than 500 ppm alkali metal.
 9. A titanium silicaliteolefin epoxidation catalyst with improved epoxidation efficiency and amean crystal size greater than 2 μm, said catalyst prepared by growingtitanium silicalite crystals in an aqueous medium containing ahydrolyzable source of titanium and a hydrolyzable silica source,wherein said hydrolyzable silica source contains less than 50 ppm ofsodium based on the weight of said silica source, said improvedepoxidation efficiency relative to a similarly prepared catalyst derivedfrom a silica source containing a higher proportion of sodium.
 10. Thecatalyst of claim 9, wherein said silica source comprises silica.
 11. Atitanium silicalite catalyst suitable for catalyzing olefin epoxidation,said catalyst comprising an intergrowth of titanium silicalite crystalshaving a mean particle size greater than 2 μm.
 12. The intergrowth ofclaim 11, wherein said intergrowth has a mean particle size of from 3 μmto about 30 μm.
 13. A process for the preparation of the intergrowth ofclaim 11, said process comprising reacting a hydrolyzable titaniumsource and a hydrolyzable silica source in the presence of atetraalkylammonium hydroxide.
 14. The process of claim 13, wherein saidtetraalkylammonium hydroxide comprises tetrapropylammonium hydroxide.15. A process for the preparation of the intergrowth of claim 11, saidprocess comprising reacting a hydrolyzable titanium source and ahydrolyzable silica source in the presence of a tetraalkylammonium saltand a base.
 16. The process of claim 15, wherein said tetraalkylammoniumsalt is a tetrapropylammonium salt.
 17. The process of claim 15, whereinsaid salt is a halide.
 18. The process of claim 15, wherein said basecomprises one or more of an organic amine, ammonia, ortetraalkylammonium hydroxide.
 19. A process for the preparation of theintergrowth of claim 11, said process comprising employing as at least aportion of said hydrolyzable titanium source and said hydrolyzablesilica source, a preformed hydrolyzable titanium/silicon copolymer. 20.The process of claim 19, wherein said hydrolyzable titanium/siliconcopolymer comprises an alkyl silicate/titanate copolymer.
 21. A processfor the preparation of titanium silicalite olefin epoxidation catalystsof improved catalytic activity, said process comprising: a) preparingtitanium silicalite crystals by crystal growth from a growth mediumcomprising a hydrolyzable silica source, a hydrolyzable titanium source,an alkylammonium salt and a base to form a titanium silicalite productcontaining crystals or intergrowths thereof having a particle sizegreater than 2 μm; b) filtering the titanium silicalite product with afilter medium having a mean pore size greater than 0.5 μm; and c)recovering a filter cake of titanium silicalite crystals or intergrowthsthereof relatively depleted of crystals or intergrowths having particlesizes less than 2 μm as compared with the amount of crystals orintergrowths with particle sizes less than 2 μm obtained in step a). 22.The process of claim 21, wherein said base is an organic amine, ammonia,or a tetraalkylammonium hydroxide.
 23. The process of claim 21, whereinsaid alkylammonium salt is a tetrapropylammonium salt.
 24. The processof claim 21, wherein said filter medium has a mean pore size of from 1μm to 8 μm.
 25. The process of claim 21, wherein said filter medium hasa mean pore size of from 2 μm to 7 μm.
 26. A process for the continuousproduction of olefin oxides, said process comprising: a) providing aslurry reactor containing titanium silicalite particles having a meandiameter greater than 2 μm as a dispersed phase in a liquid continuousphase; b) introducing into said slurry reactor an epoxidizing oxygensource comprising hydrogen peroxide, or hydrogen and oxygen; c)introducing into said reactor at least one olefin; d) withdrawing aproduct stream comprising liquid continuous phase, olefin oxide, andolefin oxide equivalents; e) separating any entrained catalyst particlesfrom said product stream prior to, during, or after separation of olefinoxide from said product stream; f) separating said olefin oxide fromsaid product stream to provide an olefin oxide product; wherein whenhydrogen and oxygen are used as said epoxidizing oxygen source, a noblemetal catalyst is further present.
 27. The process of claim 16, whereinsaid noble metal comprises one or more of Pd, Au, or Pt.
 28. The processof claim 26, wherein said titanium silicalite particles are titaniumsilicalite intergrowths having a mean particle size of from 3 μm to 30μm.
 29. The process of claim 26, wherein hydrogen and oxygen comprisethe epoxidizing oxygen source, and said noble metal is contained in oron said titanium silicalite catalyst.
 30. The process of claim 26,further comprising separating at least a portion of said liquidcontinuous phase from said product stream and recycling said at least aportion of said liquid continuous phase to the reactor as a make-upsolvent stream.
 31. The process of claim 26, wherein said liquidcontinuous phase comprises water, methanol, or a mixture of water andmethanol.
 32. The process of claim 26, wherein an alkali or metal orammonium carbonate or bicarbonate are additionally introduced into saidreactor.
 33. The process of claim 26, wherein said olefin comprisespropylene.
 34. The process of claim 26, wherein said noble metalcomprises palladium, gold, or platinum, or mixtures thereof.
 35. Theprocess of claim 26 wherein an ammonium phosphate or ammonium hydrogenphosphate or mixture thereof are introduced into said reactor.